Why not just model zonal heat pumps with the ZoneHVAC:PackagedTerminalHeatPump object?

The COP will be dependent on the outdoor air temperature and load, so you can't just take a rated COP and apply it to the total sensible load. You'd need to know the heat pump performance curves and apply them. Doable in a spreadsheet, but EnergyPlus does this calculation for you.

Also, a dehumidifier acts on air within a zone, which will be at a different temperature and humidity level than the input to the heat pump if it includes outdoor air ventilation. The ratings are based on a consistent zone temperature, not on outdoor air as well, so you can't just use them directly on outdoor air. Is the intent to capture latent cooling of just the outdoor air, or outdoor air and space latent loads as well?

Depending on your cooling coil leaving temperature, the coil will provide dehumidification, meaning sensible and latent cooling go together unless less there is a dedicated desiccant-based separate sensible and latent cooling (SSLC) system.

Assuming somehow the system is SSLC with a zone dehumidifier rated in terms of L/kWh, the energy to meet the latent component can be calculated by [latent cooling load (kJ)]* [1 / latent heat of water (kJ/kg)] * [1 / density of water (kg/m3)] * [1000 (L/m3)] * [1 / energy factor(L/kWh)]. Note the latent cooling load here is the zone latent load, not the load from the ideal loads air system (unless there is no outdoor air).